基于集合预报的四川夏季强降水订正试验

CALIBRATION OF THE ENSEMBLE-BASED FORECAST OF SUMMER HEAVY RAINFALL IN SICHUAN

四川历来多暴雨洪涝,然而其发生具有很多不确定的因素,预报难度很大。从观测与模式预报的累积概率密度函数角度出发,利用2007—2012年6—8月中国降水观测格点资料和2012—2013年6—8月ECMWF模式集合预报资料,探索了一种提高四川地区强降水预报准确率的方法——概率阈值订正法,并运用该方法对2012年6—8月盆地东部的降水过程进行批量试验。试验结果表明:订正后的模式预报相比订正前的预报而言,不仅强降水落区更接近实况,而且较大程度地延长了预报时效,能提前6~7天给出强降水过程的警示信息,经过订正后显著提升了ECMWF模式的降水预报水平。

Because of many uncertain factors, it is difficult to forecast the heavy rainfall-caused floods which happen easily in Sichuan Province. From the cumulative distribution function of the observations and model forecasts, a method that improves the forecast accuracy of heavy rainfall in Sichuan was developed by using the observed rainfall data in June-August during 2007-2012 and the ECMWF ensemble forecast precipitation data in June-August of 2012-2013. It was applied to an experiment of extreme rainfall events in June-August of 2012 in eastern Sichuan Basin. The results show that after calibration, the heavy rain area is more similar to the observation and the forecast period is greatly extended, which is useful for issuing early warnings of heavy rain processes 6-7 days in advance. In short, the method can significantly improve the forecast with the ECMWF model in eastern Sichuan Basin.